Polymer-thickened solutions are used for many purposes in the field of drilling and completing oil and gas wells. When wells are gravel-packed, polymers are usually incorporated in the gravel pack composition to improve the suspension of gravel pack solids. U.S. Pat. Nos. 5,027,899; 5,058,677; 5,184,679; and 5,251,699 describe exemplary gravel packing processes. Polymers can also be used as thickeners in conjunction with formation acid treatment. U.S. Pat. Nos. 3,779,914; 4,487,265; and 5,007,481 disclose exemplary acid treatment methods that utilize such polymers.
Well completion and workover fluids designed to have fluid loss control properties often contain polymer thickeners to reduce fluid loss by increasing the low-shear viscosity. U.S. Pat. Nos. 4,369,843; 4,502,969; 4,620,596; and 4,621,692 disclose compositions that are exemplary.
When these compositions are prepared at a wellhead location, they are typically prepared in large batches, with the polymers added to large tanks equipped with paddle stirrers and recirculation pumps. Providing such equipment can be relatively expensive, and mixing large volumes of viscous solutions can be very time-consuming. These problems are particularly evident when the polymer-thickened composition is to be used in an offshore operation because offshore platforms have limited space and limited allowed deck loads.
When polymer-thickened compositions are prepared at wellhead locations by batch mixing, it is not uncommon for the final composition to be of less than desirable consistency. If polymer concentrates are not hydrated fully, "fish eyes" of unhydrated polymers form. These fish eyes can significantly impair permeability into the wellbore. To provide adequate mixing between the polymers and the carrier fluids, the solutions are often circulated by pumps to provide some shearing and mixing. Pumps used for circulating the polymer-thickened solutions often shear and degrade the polymers, resulting in the polymer being less effective as a thickener.
It is therefore an object of the present invention to provide a method to produce a polymer-thickened fluid wherein the polymer-thickened fluid is produced continuously and is produced in a fully hydrated form. It is another object of the present invention to provide such a method wherein a homogenous thickened fluid is prepared. It is a further object to provide such a method wherein the mixing of the polymer into the polymer-thickened solution does not result in degradation of the polymer.